This invention relates to a wellhead connector and a method of connecting a wellhead connector to a casing.
The lower part of a wellhead is called a casing head or tubing head, hereafter termed casing head. The casing head is attached to a casing (tubular pipe) and provides a connection at its upper end to the wellhead equipment located there above. The connection must be able to seal well pressure and transmit mechanical loads in any direction. Common connections to a casing are either by threading or by welding. The problems with these methods of attaching the casing head are that they may require extensive time and labour, are often expensive, and create the possibility of installation errors. Also, experienced welders may not be available at the well site.
Another method is to attach the casing head using a means for gripping the casing pipe with mechanically activated teeth. A seal between the casing head and the casing pipe is then provided separately, usually in the form of an elastomeric seal ring (for example an O-ring) located in the casing head above a mechanical gripping mechanism. Such an assembly is well known in the industry and is described in, for example, U.S. Pat. No. 4,799,714 issued to Collet, U.S. Pat. No. 5,332,043 issued to Ferguson, and Canadian Patent 2,015,966 issued to Anderson et al. Each of these patents describes a known method for mechanically attaching the casing head to the surface casing. These patents disclose the use of conical slip segments which surround the casing pipe, each slip segment being provided with a plurality of grooves on their straight inside surface (casing pipe-contacting surface) that act as teeth that bite into the outer surface of the casing. A slip housing, or actuation sleeve, with a conical mating surface to the conical surface on the outside of the slip segments is driven against the slip segments (or the slip segments are driven against the slip housing/sleeve). This forces the slip segments against the surface casing pipe causing the grooves to frictionally grip (or the teeth to bite into) the casing pipe, and thus to secure the casing pipe to the casing head. These slip segments are commonly referred to as “slips” and the system is commonly described as a slip lock casing connector, or slip connector.
A slip lock casing connector has advantages over the previously described casing connectors. These include reduced installation time compared to welding, and unlike a threaded connection, proper orientation of the head can be achieved.
Other casing head connections for oil and gas wellheads can be seen in the following U.S. Pat. No. 4,239,266 to Mynhier; U.S. Pat. No. 4,304,424 to Hanson; U.S. Pat. No. 4,936,382 to Thomas; U.S. Pat. Nos. 5,135,266; 5,158,326 to Anderson et al.; U.S. Pat. No. 5,205,356 to Bridges et al.; U.S. Pat. No. 5,299,644 to Ekert; U.S. Pat. No. 5,899,507 to Schroeder et al.; and U.S. Pat. No. 6,834,718 to Webster.